Electrochemical exfoliation of 2d materials

ABSTRACT

A method for the production of non-carbon-based 2D materials and/or non-carbon-based 2D material nanoplatelet structures having a thickness of less than 100 nm in an electrochemical cell having a negative electrode which comprises a non-carbon-based bulk 2D material and an electronically conducting material such as a metal.

This application claims priority from GB1521056.0 filed 30 Nov. 2015,the contents of which are incorporated herein in their entirety.

FIELD OF INVENTION

The present invention relates to a method for the production of 2Dmaterials and related nanoplatelet structures.

BACKGROUND

Since the discovery of the remarkable physical properties and chemicalstability of graphene, two-dimensional (2D) nanomaterials have attractedsignificant interest, becoming one of the most active research areas ofmaterials science. The study of 2D materials was originally dominated byresearch into clays and later oxides but now extends beyond graphene tomaterials such as hexagonal boron nitride (h-BN), transition metalchalcogenides (TMCs) and carbides (MXene materials that are related tobulk MAX phases).

A common feature of these 2D nanomaterials is that they have strong(in-plane) covalent bonds within each layer but interact with adjacentlayers via weak bonds, leading the sheets to stack into 3-dimensionalbulk crystals.

Currently, 2D nanomaterials are produced via bottom-up growth by methodssuch as chemical vapor deposition or by top-down approaches such asmicromechanical cleavage or liquid exfoliation of the bulk layeredcrystals by ultra-sonication. However, these routes are unable toproduce large quantities and/or the products suffer from very smallsheet size, making them unsuitable for many applications such as energystorage, composites, and catalysis.

DESCRIPTION OF THE INVENTION

Herein, a simple and scalable approach is introduced, in which theexfoliation of the layered compounds is driven by gentle electrochemicalreactions. While electrochemical exfoliation of graphite to producegraphene has been reported by the present inventors (including, forexample, WO2012/120264, WO2013/132261, and WO2015/019093, each of whichis incorporated by reference in its entirety), the special electronicproperties of other 2D materials can preclude this type of exfoliation;as the materials are insulators or semi-conductors, electronicintercalation and subsequent exfoliation cannot be readily used.

The present inventors have found that, through the provision of acomposite electrode comprising the bulk 2D material to be exfoliated andan electronically conducting material such as a metal, this problem canbe overcome. Surprisingly, the presence of the metal in the compositebody of the electrode enables efficient intercalation between thestacked 2D layers to provide efficient exfoliation and excellent monoand few layer non-carbon-based 2D materials. This has been demonstratedeven with bulk 2D materials which are known to be good insulators suchas h-boron nitride.

Without wishing to be bound by any particular theory, the inventorsattribute the efficient exfoliation at least in part to the presence ofthe metal lowering the current needed to effect the intercalation, evenin cases where the non-carbon-based 2D material is a semi-conductor.Lower currents reduce electricity consumption, may reduce the occurrenceof unwanted side effects and may be safer to scale commercially.

The resultant 2D crystals are significantly larger in size than anyreported wet-chemical technology for mass production of 2D materials.Many of these materials are readily dispersible in various organicsolvents such as NMP and DMF and offer a variety of potential uses.

The present invention relates to methods for the production of 2Dmaterials and 2D material nanoplatelet structures from non-graphiticsources. The 2D materials produced are not graphene or functionalizedgraphene.

In a first aspect, the present invention provides a method for theproduction of non-carbon-based 2D materials and/or non-carbon-based 2Dmaterial nanoplatelet structures having a thickness of less than 100 nmin an electrochemical cell, wherein the cell comprises:

(a) a negative electrode which comprises a non-carbon-based bulk 2Dmaterial and an electronically conducting material;

(b) a positive electrode; and

(c) an electrolyte;

and wherein the method comprises the step of passing a current throughthe cell.

During the step of passing the current through the cell, thenon-carbon-based bulk 2D material is electrochemically exfoliated toafford non-carbon-based 2D materials and/or non-carbon-based 2D materialnanoplatelet structures having a thickness of less than 100 nm.

It will be appreciated that the non-carbon-based bulk 2D material andelectronically conducting material are suitably provided as an admixtureor composite of flakes or powders.

The negative electrode is the electrode held at the most negativepotential out of the two electrodes. The negative electrode is commonlyreferred to in electrochemistry as the cathode.

A reference electrode may also be used.

Suitably, the electrode comprising a non-carbon-based bulk 2D materialand an electronically conducting material (e.g a metal) is provided as acomposite comprising a binder. Suitable binders include polymers. Forexample, polyvinyl alcohol (PVA), cellulose, polyaniline (PANI), andpolyvinylidene fluoride (PVDF). It will be appreciated that suitablepolymers may include those that are known to be soluble in water orother solvents, which may aid isolated of the final product.

The electrode may be provided as an admixture of a non-carbon-based bulk2D material and an electronically conducting material (e.g. a metal) ina membrane or mesh, reducing or obviating the inclusion of a binder.

Suitably, the electronically conducting material is a metal. Suitably,the metal is a transition metal.

Preferably, the electronically conducting material is ferromagnetic.This assists removal of after exfoliation (a suspension of theexfoliated material may simply be stirred with a magnetic flea, to whichthe particles attach). Suitable ferromagnetic materials include iron,nickel and cobalt. Suitable alloys may also be used. In some cases, themetal is nickel.

In some cases, the method includes the step of preparing the electrodecomprising a non-carbon-based bulk 2D material and an electronicallyconducting material such as a metal. The method may comprising forming apellet comprising a bulk 2D material powder, the electronicallyconducting material (e.g. metal) and a binder. Suitably, the methodcomprises:

-   -   i. forming a slurry of a bulk 2D material, an electronically        conducting material (e.g. a metal) and a binder in a solvent        (for example, an alcohol such as ethanol);    -   ii. optionally milling the slurry, for example using alumina        milling media;    -   iii. drying the slurry to obtain a powder;    -   iv. pressing the powder of step iii to form a pellet, for        example, using a hydraulic press;    -   v. sintering the pellet of step iv.

Suitably, the bulk 2D material and electronically conducting material(e.g. metal) are provided as powders.

Suitably, the sintering step takes place at 150° C. or more, preferablyat 200° C. or more; more preferably at 250° C. or more. For example, thepellet may be sintered under argon at about 300° C.

In a further aspect, the invention provides a pellet comprising anon-carbon-based bulk 2D material powder, an electronically conductingmaterial (e.g a metal) and a binder, for example, a pellet obtainablefrom steps i to v.

In a further aspect, the invention provides a method of preparing apellet comprising a non-carbon-based bulk 2D material and anelectronically conducting material (e.g a metal), the method comprisingsteps i to v detailed above.

In a further aspect, the present invention provides a non-carbon-based2D material or nanoplatelet structure obtainable by a method asdescribed herein.

It will be appreciated that all options and preferences are combinable,except where context dictates otherwise. For example, options andpreferences relating to the method apply equally to pellet and viceversa.

Definitions

2D Material

In the present application, the term “2D material” is used to describematerials consisting of ideally one to ten layers, preferably where thedistribution of the number of layers in the product is controlled. Themethod can also be used to make 2D nanoplatelet structures under 100 nmin thickness, preferably under 10 nm in thickness and more preferablyunder 1 nm in thickness. The size of the flakes produced can vary fromnanometres across to millimetres, depending on the morphology desired.

In some aspects of the invention, the material produced is a 2D materialhaving up to ten layers. The 2D material produced may have one, two,three, four, five, six, seven, eight, nine or ten layers.

In other aspects of the invention, the material produced may comprise atleast 10% by weight of 2D material having up to ten layers, preferablyat least 25% by weight and more preferably at least 50% by weight of 2Dmaterial having up to ten layers.

In some cases, the method produces primarily or only non-carbon-based 2Dmaterials. In other cases, the method produces both non-carbon-based 2Dmaterials and/or non-carbon-based 2D material nanoplatelet structureshaving a thickness of less than 100 nm. It will be appreciated that,under certain conditions, the method may produce primarilynon-carbon-based 2D material nanoplatelet structures having a thicknessof less than 100 nm. In other words, the average number of layers of thematerial produced may vary from mono and few layer to 10 or more layers.

Non-Carbon-Based 2D Material

Carbon-based 2D materials are becoming increasingly well-known. Theyfeature sheets of fused six-membered carbocyclic rings in a honeycombarrangement. The most famous carbon-based 2D material is graphene, whichis composed of planar sheets of unsaturated carbocyclic rings (benzenes)with a delocalised π electron system over the entire sheet. Carbon-based2D materials may also contain non-carbon groups, and the termcarbon-based 2D materials includes these partially saturated andentirely saturated compounds. For example, graphane is a saturatedcarbon-based 2D material comprising sheets of fused 6-memberedcarbocycles in which each carbon bears a hydrogen atom. Both 1-sided and2-sided graphane are known. Other carbon-based 2D materials include,without limitation, graphene oxide and fluorographene.

Non-carbon based 2D materials do not include carbocyclic rings. Examplesof non-carbon-based 2D materials include hexagonal boron nitride (h-BN),transition metal chalcogenides (TMCs), and metal carbides.

In some cases, the non-carbon-based 2D material of the present inventionis 2D h-BN. In some cases, the non-carbon based 2D material of thepresent invention is a transition metal dichalcogenide (TMDC). ExemplaryTMDCs include, without limitation, molybdenum disulfide (MoS₂), tungstendisulfide (WS₂), molybdenum diselenide (MoSe₂) and tungsten diselenide(WSe₂). In some cases, the non-carbon based 2D material of the presentinvention is a disulfide, for example, MoS₂ or WS₂.

Bulk 2D Material

A bulk 2D material comprises many layers of 2D material stacked and heldtogether with weak forces. For example, graphene is a 2D material, whilegraphite is the corresponding bulk 2D material held together with Vander Walls forces. In the context of the present invention, bulkmaterials are used in the electrode that undergoes exfoliation.Exfoliation affords 2D materials and/or 2D material nanoplateletstructures. It will be appreciated bulk materials comprise many hundredsof layers, typically many thousands of layers.

Cathode

The term cathode is used to refer to the negative electrode.

The cathode comprises a bulk non-carbon-based 2D material and anelectronically conducting material. Suitably, the electronicallyconducting material is a ferromagnetic metal such as nickel. The w/wratio of bulk 2D material to electronically conducting material may be5:1 to 1:1, for example 3:1 to 1:1, for example, 2.5:1 to 1.5:1. In somecases, the w/w ratio is about 2:1.

Suitably, the electronically conducting material is provided as apowder. For example, the powder may be μm-sized or smaller, for example<1 μm.

Electrolyte

Suitable electrolytes are known in the art and include those describedin WO2014/191765 (which is herein incorporated by reference in itsentirety for all purposes, and in particular the section entitledelectrolytes beginning on page 15).

Suitable electrolytes include salt solutions, molten salts, and ionicliquids such as eutectic systems. Salt solutions may be solutions inaqueous solvents, in organic solvents or in eutectic solvents. Eutecticsystems are ionic liquids formed of a mixture of compounds having amelting point lower than that of the individual components. In somecases, the melting point of the eutectic system is at least 25° C. lowerthan that of lowest melting point component, for example at least 50° C.lower, at least 75° C. lower, preferably at least 100° C. lower.Eutectic systems and solvents and may include, for example, cholinechloride (ChCl):Urea (1:2 M ratio), ChCl:Ethylene glycol (1:2),ChCl:Glycerol (1:2), ChCl:Malonic acid (1:1), ChCl:CrCl₃.6H2O (1:3),ChCl:ZnCl₂ (1:2), ZnCl₂:Urea (1:3.5), Ethylammonium chloride:Acetamide(1:1.5), EMC:Ethylene glycol (1:3), EMC:Glycerol (1:3), MPB:Ethyleneglycol (1:3), MPB:Glycerol (1:3)

In some cases, the electrolyte is a solution of an inorganic salt suchas LiCl or an organic salt such as an alkylamine salt, for exampletrimethylamine hydrochloride or trimethylamine hydrochloride. Naturally,mixtures of salts may be used. Suitable solvents may include DMSO. Insome cases, the solvents are eutectic solvents. For example, theelectrolyte may be a salt such as LiCl dissolved in a eutectic solventsuch as a urea:choline chloride mixture (typically in a 2:1 mole ratio).

In some cases, the electrolyte is a molten salt, for example NaCl orLiCl may be used so that the material can exfoliated at hightemperatures of 600° C.+. It will be appreciated that the stability ofthe 2D material to be produced should be considered in selecting anupper temperature (as some are known to be unstable at hightemperatures).

In these cases the electrode's binder may be pyrolised prior to use toincreases its structural stability at this elevated temperatures.

In some cases, the electrolyte is a eutectic system. For example, theelectrolyte may be a eutectic mixture of a quaternary ammonium salt anda metal chloride. Suitable examples are provided above.

Positive Electrode

This is referred to as the anode.

The positive electrode may consist of any suitable material known tothose skilled in the art as it does not play a role in the materialproduction, other than to provide a counter electrode for the anions.Preferably, the positive electrode is made from an inert material suchas gold, platinum or carbon. In further embodiments, the positiveelectrode may be made of a material that oxidises to give the metal ionsin the electrolyte, such as lithium.

When the reaction at the positive electrode generates a gas theelectrode surface area is as large as possible to prevent gas bubbleswetting it and/or disrupting the process at the negative electrode. Thepositive and/or reference electrode may also be placed in a membrane ormolecule sieve to prevent undesired reactions in the electrolyte or ateither electrode. The positive and the negative electrodes couldalternatively be placed in a two-compartment cell, wherein eachcompartment contains one electrode, and the compartments are connectedthrough a channel.

Cell Potential and Current Density

The working potential of the cell will be at least that of the standardpotential for reductive intercalation. An overpotential may be used inorder to increase the reaction rate and to drive the cations into thegalleries of the graphite at the negative electrode. Preferably anoverpotential of 1 mV to 10 V is used against a suitable reference asknown by those skilled in the art, more preferably 1 mV to 5 V. Incells, with only two terminals, and no reference, a larger potential maybe applied across the electrodes but a significant amount of thepotential drop will occur over the cell resistance, rather than act asan overpotential at the electrodes. In these cases the potential appliedmay be up to 20V or 30V.

The voltage applied across the electrodes may be cycled or swept. In oneembodiment, both the electrodes comprise a non-carbon-based bulk 2Dmaterial and a metal and the potential is swept so that electrodeschange from positive to negative and vice versa. In this embodiment thecationic exfoliation would occur at both electrodes, depending on thepolarity of the electrode during the voltage cycle. In some embodiments,alternating current can be used to allow for both fast intercalationsand de-intercalations.

The current density at the negative electrode may be controlled usingmethods as are known in the art.

In some methods according to the invention using MoS₂/Ni cathodes, atvoltage of 10 V was set. The current range typically varied over therange 2-30 mA. The inventors observed that the current using MoS₂/Nicathodes was higher than attempts to exfoliate MoS₂ only cathodes. Thedifference was significant, even at the small experimental scales. Thismeans that, even for certain semi-conducting bulk materials for whichexfoliation may be possible, there are economic and environmentalbenefits to the methods of the invention.

Operating Temperature

The cell is operated at a temperature which allows for production of thedesired material.

The cell may be operated at a temperature of at least 10° C., preferablyat least 20° C. The maximum cell operating temperature may be 100° C.,and more preferably 90° C., 80° C., 70° C. or 50° C. In someembodiments, the cell may be operated at a temperature of at least 30,40, 50, 75, 100, 150 or even 200° C. The maximum cell operatingtemperature may, in some cases, be as high as 250° C. The optimumoperating temperature will vary with the nature of the electrolyte.Operating the cell up to the boiling point of the electrolyte may becarried out in the present invention, keeping in mind the temperaturestability of the desired product.

Recovery of Cations

In one embodiment, the cations used for the exfoliation are recoveredafter exfoliation. The cations may be recovered by washing and/orheating of the exfoliated material, electrochemical reduction of thecations, ultrasonic energy treatment of the exfoliated material,displacement from the exfoliated material by surfactants or combinationsthereof.

The non-carbon-based 2D materials and non-carbon-based 2D materialnanoplatelet structures having a thickness of less than 100 nm producedby the method of the invention may be separated from the electrolyte bya number of separation techniques, including:

(a) filtering;

(b) using centrifugal forces to precipitate the non-carbon-based 2Dmaterials and non-carbon-based 2D material nanoplatelet structures;

(c) collecting the non-carbon-based 2D materials and non-carbon-based 2Dmaterial nanoplatelet structures at the interface of two immisciblesolvents; and

(d) sedimentation.

The electrochemically exfoliated non-carbon-based 2D materials andnon-carbon-based 2D material nanoplatelet structures may be furthertreated after exfoliation. For example, the materials may be furtherexfoliated using ultrasonic energy and other techniques known to thoseskilled in the art to decrease the flake size and number of layers.

In some embodiments, the electrochemical intercalation may be repeatedin order to achieve full exfoliation.

Analysis of the Material

It is well established in the literature that Raman spectroscopy can beused to measure the number of layers that a graphene flake possessesthrough the shape, intensity and position of the peaks. In a similarway, non-carbon-based 2D materials may be analysed using Ramanspectroscopy. TEM and AFM images may also be used to determine flakesize.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a TEM image of the solution produced in example 1spray-coated on silicon wafer and subjected to AFM analysis to confirmthe exfoliation.

FIG. 2 shows the Raman spectra of the bulk (lower) and exfoliated(upper) MoS₂ of Example 1.

FIG. 3 shows an AFM image and measurements of a representativeexfoliated flake of Example 2.

FIG. 4 shows the Raman spectra of exfoliated (lower) and bulk (upper)MoS₂ using a 633 nm excitation. The exfoliated material was obtained inexample 2.

FIG. 5 shows an AFM image and measurements of a representativeexfoliated flake of Example 3.

FIG. 6 shows an AFM image and measurements of a representativeexfoliated flake of Example 4.

FIG. 7 shows a TEM image of an exfoliated WS₂ nanosheet of Example 4 andthe corresponding selected area electron diffraction (SAED) patterns.

EXAMPLES

The following examples are provided to illustrate the invention and arenot intended to limit the invention.

Exemplary Electrode Preparation:

About 2 g of MoS₂ and 1 g of Ni powder (<1 μm, 99.8% trace metals basis)were mixed in ethanol with 0.2 g PVA as a binder in a 500 ml bottle.Alumina milling media was added to the mixture and the slurry was ballmilled for 2 hours to achieve good homogeneity. The alumina spheres werethen separated from the slurry using metallic sieves. The slurry wasthen allowed to dry over night until the powder was visibly dry thendried further under vacuum for 4 hours. After drying the powder mixturewas pressed into a 20 mm diameter pellet using a uniaxial hydraulicpress, and then sintered under argon at 300° C.

Electrodes of WS₂ and other layered materials were prepared usingsimilar protocols.

Electrochemical Exfoliation:

A cell was assembled with the MoS₂ pellets as cathode, and Pt wire asanode. The liquid electrolyte was prepared by dissolving lithiumchloride (Sigma Aldrich, 99.9%) and/or triethylamine hydrochloride indimethyl sulfoxide (DMSO Sigma Aldrich, 99.9%). A potential of 10 V wasapplied for 10 hours.

After electrolysis, the clear transparent electrolyte changes color todark green due to suspension of the MoS₂ flakes in the electrolyte. Thesuspension (about 30 ml) was then mixed with 2 L of water and stirredfor 2 hours using a magnetic stirrer. During the stirring process, theNi powder attached to the magnet, leaving the supernatant free of Ni.The solution was then centrifuged at 5000 rpm and the supernatant wasdecanted. The remaining powder was dried overnight under vacuum at 60°C.

The powder was then suspended in NMP by mild sonication for 20 minutesand diluted with ×30 isopropanol by volume. The solution was thenspray-coated on a silicon wafer and subjected to AFM analysis to confirmthe exfoliation. Flakes with a thickness of ˜1-3 nm were observed on theAFM images, indicating MoS₂ was exfoliated down to monolayer and fewlayers (FIG. 1). The size of the nanosheets ranged from 0.5 to 3 micron,which is 5-10 orders of magnitudes higher than the MoS₂ flakes producedby any previously reported liquid exfoliation method.

Raman analysis also confirmed the exfoliation of the bulk MoS₂. FIG. 2shows the Raman spectra of the bulk and exfoliated MoS₂. Both materialsshowed 2 bands at ˜380 (A_(1 g)) and ˜405 (E¹ _(2 g)) cm⁻¹. However, thedifference between the 2 bands reduced from ˜27 cm⁻¹ for the bulk to ˜23cm⁻¹ for the exfoliated materials. The intensity of the bandssignificantly enhanced after the exfoliation. Also full-widths athalf-maximum values are obviously increased in the exfoliation productsthan in the bulk samples, which may be possibly attributed to phononconfinement by facet boundaries.

Example 2

Similar to example 1 but the electrolyte used was 0.5 M LiCl dissolvedin a eutectic mixture of urea choline chloride (2:1 mole ratio of urea:choline chloride). FIG. 3 shows an AFM image of a representative exampleof the exfoliated flake. FIG. 4 shows the Raman spectra of exfoliated(lower) and bulk (higher) MoS₂ using the 633 nm excitation. It is clearthat the bands of the exfoliated samples are different to that of thebulk material both in terms of Raman frequency and signal intensity. Forthe exfoliated sample, two strong Raman bands, deconvoluted by a singleLorentzian centered at 383 cm⁻¹ and 407 cm⁻¹, were assigned to in-planeE¹ _(2 g) and out-of-plane A_(1 g) vibrational modes, with no evidenceof structural distortion, inferring the absence of structural damageand/or covalent bond formation upon the electrochemical exfoliation.Unlike the bulk MoS₂, the A_(1 g) and E¹ _(2 g) modes for exfoliatedMoS₂ appeared with equal intensities, indicating weaker coupling betweenthe electronic transition at the K point with the A_(1 g) phononexisting in MoS₂ nanoplatelet. The frequency difference between A_(1 g)and E¹ _(2 g) was measured to be 24 cm⁻¹. The value of this differencefor the bulk material was found to be 27 cm⁻¹, signifying the success ofexfoliation and the existence of MoS₂ in few layers.

Example 3

Similar to example 1, but the electrode was fabricated from h-BN powder.The thickness of the obtained flake as measured by the AFM was below 5nm for 80% of the flakes measured (FIG. 5).

Example 4

Similar to example 1, but the electrode was fabricated from WS₂ powder.The AFM confirmed the exfoliation of the bulk materials to few layersWS₂ (FIG. 7). The TEM image of exfoliated WS₂ nanosheets and thecorresponding selected area electron diffraction (SAED) patterns areshown in FIG. 7 which indicate that the exfoliated TMDC materials stillhave a hexagonal lattice structure.

Characterisation

Raman spectra were obtained using a Renishaw system 1000 spectrometercoupled to a He—Ne laser (633 nm). The laser spot size was ˜1-2 μm, andthe power was about 1 mW when the laser is focused on the sample usingan Olympus BH-1 microscope. The SEM images were taken using a Zeiss Leo1530 FEGSEM. TEM analysis was conducted using FEI Tecnai FZO 200 kvFEGTEM.

All patents, applications, and other publications cited herein areincorporated by reference in their entirety for all purposes.

1. A method for the production of non-carbon-based 2D materials and/ornon-carbon-based 2D material nanoplatelet structures having a thicknessof less than 100 nm in an electrochemical cell, wherein the cellcomprises: (a) a negative electrode which comprises a non-carbon-basedbulk 2D material and an electronically conducting material; (b) apositive electrode; and (c) an electrolyte; and wherein the methodcomprises the step of passing a current through the cell.
 2. The methodof claim 1, wherein the electronically conducting material is a metal.3. The method of claim 1, wherein the electronically conducting materialis ferromagnetic.
 4. The method of claim 1, wherein the electronicallyconducting material is nickel.
 5. The method of claim 1, wherein themethod produces hexagonal boron nitride and/or hexagonal boron nitridenanoplatelet structures.
 6. The method of claim 1, wherein the methodproduces 2D transition metal dichalcogenide and/or transition metaldichalcogenide nanoplatelet structures.
 7. The method of claim 6,wherein the transition metal dichalcogenide is MoS2 or WS2.
 8. Themethod of claim 1, wherein the method includes the step of preparing theelectrode comprising a non-carbon-based bulk 2D material and anelectronically conducting material, the method comprising: i. forming aslurry of the bulk 2D material, the electronically conducting materialand a binder in a solvent; ii. optionally milling the slurry; iii.drying the slurry to obtain a powder; iv. pressing the powder of stepiii to form a pellet; v. sintering the pellet of step iv.
 9. A method ofpreparing a pellet for use as a cathode comprising a non-carbon-basedbulk 2D material and an electronically conducting material, the methodcomprising: i. forming a slurry of the bulk 2D material, theelectronically conducting material and a binder in a solvent; ii.optionally milling the slurry; iii. drying the slurry to obtain apowder; iv. pressing the powder of step iii to form a pellet; v.sintering the pellet of step iv.
 10. The method of claim 9, wherein thebinder is a polymer, optionally wherein the binder is apolyvinylalcohol.
 11. The method of claim 9, wherein the electronicallyconducting material is ferromagnetic.
 12. A pellet for use as a cathodecomprising a admixture of non-carbon-based bulk 2D material and anelectronically conducting material in a binder.
 13. The pellet of claim12, wherein the electronically conducting material is ferromagnetic. 14.A non-carbon-based 2D material or nanoplatelet structure obtainable by amethod according to claim
 1. 15. The method of claim 8, wherein thebinder is a polymer, optionally wherein the binder is apolyvinylalcohol.
 16. The method of claim 10, wherein the electronicallyconducting material is ferromagnetic.